The present invention relates to an apparatus comprising a bedplate and doctor blade assembly which enables the production of a uniform coating on the back of a web of material, such as, for example, on the back of an unfinished carpet, turf or textile. This is achieved by means of a recess in the bedplate from a position upstream of the doctor blade assembly to a position downstream of the doctor blade assembly over which the web of material crosses while maintaining tension on the web of material.
Doctor blade assemblies and bedplates are known to be particularly useful in the field of carpet manufacturing. Carpets are generally produced by tufting carpet yarns into a primary backing, the tufts being secured in the primary packing through use of a precoat, a foam, or a tuftbind adhesive. This carpet without a precoat of tuftbind adhesive is typically referred to as a greige good. The greige good is optionally coated with adhesive and secured to a secondary backing, generally of polypropylene or jute. Key properties of the carpeting produced by these processes are tuft bind, i.e. the strength required to pull tufts from the primary backing, and delamination strength, i.e., the force required to separate the secondary backing from the carpet.
The manufacture of carpet by implanting tufts in an adhesive composition spread on a backing material is known and described, for example, in British Patent 1,121,036, the disclosure of which is herein incorporated by reference. This requires the adhesive to be applied to a moving web of backing material in such a way as to form a uniform layer. A doctor blade, also commonly referred to as a doctor bar, is typically used to spread the adhesive or coating into a layer on the back of the greige good. In order to accommodate variations in the thickness of the greige good, backing material and/or in the desired adhesive layer, the doctor blade is mounted in an adjustable manner that allows it to be moved towards and away from a structural element (i.e., a bedplate) over which the web of material passes.
Carpets and artificial turfs are typically produced in widths about 12 to about 15 feet, but can be wide as up to about 18 feet. The manufacturing process requires that the doctor blade be about the same length as the width of the carpet, i.e., about 12 to 15 feet and possibly about 18 feet. This is necessary to enable the doctor blade to span the width of the carpet as it passes underneath the blade. The doctor blade is normally built up from one or more machined sections secured to a supporting truss or other suitable supporting means (e.g., an I beam). In order to maintain the edge of the blade accurately across the width of the web of material or greige good, the supporting truss is usually rather large, and considerable strength is required to adjust the mechanism.
U.S. Pat. No. 5,036,793 describes a doctor blade apparatus in which the adjustment means is simplified. A gap of pre-determined height is defined between the doctor blade and the bedplate to allow the web of material to pass through, and the height of this gap is adjusted by a means comprising an actuator for moving the base member (or bedplate) towards and away from the doctor blade assembly. This actuator comprises one or more jacks spaced along the base member which are preferably operable simultaneously to move the base member closer to (i.e., higher) or farther from (i.e., lower) the doctor blade assembly. Worm drive jacks connected to a common worm drive shaft are used.
Unfortunately, the apparatus of U.S. Pat. No. 5,036,793 does not allow one to produce a greige good without the same pattern that appears on the face of the greige good appearing in the coating layer that is applied to the back of the greige good.
The present invention differs from that described in U.S. Pat. No. 5,036,793 which requires that the entire bedplate is moved in relation to the doctor blade apparatus. By comparison, the present invention requires a change in the height of the bedplate from a position slightly upstream of the doctor blade to a position slightly downstream of the doctor blade such that a gap or recess is present/formed in this area. As the web of material passes over this recess, this recess allows the face fibers of the greige good to fall down into the gap or recess, thus relieving some of the pressure the face fibers put on the doctor blade, and allows the formation of a relatively uniform coating weight to be formed on the back surface of the web of material. This is particularly useful when the greige good has a pattern on the face, i.e., when the face fibers of the greige good are of varying lengths (i.e., uneven). It is also useful, when, for example, a berber carpet is being produced or for the production of artificial turf wherein the face fibers of the greige good are different lengths.
Advantages of the present invention include the fact that the present invention provides better coverage of the web of material or greige good with a thin layer of precoat, foam, tuftbind adhesive, etc., which is applied to the back surface of the web of material. The present invention allows for the production of finished carpeting articles having a relatively uniform back coating, which means that the back coating is relatively consistent in terms of the coating weight applied to the web of material. Less coating material is required by the present invention, and thereby results in cost savings in the manufacturing process.